Ultrafast Multi-GHz Waveguide Lasers

Lead Research Organisation: University of Southampton
Department Name: Optoelectronics Research Centre

Abstract

In this work we will develop very compact and efficient laser sources with a footprint of just a few square centimetres that are capable of producing more than a billion pulses of light per second, each having a duration of less than one tenth of one trillionth of a second. Such sources have a wide range of applications, including microscopy of biological cells, precise measurement of optical frequencies, spectroscopy and telecommunications, which can all take advantage of both the very short duration of the pulse and its high repetition rate. Many of these applications currently rely on large and relatively inefficient lasers which necessarily limits application design. The miniaturised sources that we propose are based on a waveguide geometry that confines the laser light to very small dimensions, in a similar fashion to that used in glass optical fibres. However, these waveguides are based in crystals such as titanium-doped sapphire and ytterbium-doped tungstate, which have proven themselves capable of providing the very short pulses of light that we are interested in. The waveguide geometry is also capable of supporting components that are integrated into one monolithic device that can both act as the laser gain material necessary to generate the light and provide the ultrafast switching that is required to give short pulses. The waveguides will be fabricated by growing thin layers of doped crystal on undoped substrates, with the dopant providing both the laser gain and the refractive index increase necessary to confine the light to the thin layer. Advanced waveguide structures, based on etching of these layers and re-growth, will be fabricated to give optimum laser performance and allow pumping by high-power diode lasers. The integrated switching components will be based on saturable absorbers that give low loss for high-intensity short optical pulses and high loss for low-intensity continuous wave light. Optimisation of the switching properties of these absorbers and their integration with the waveguide laser will form a major part of this work. We will also investigate the use of the Kerr effect in simple thin-film waveguides to achieve short optical pulse production by using laser resonator designs that take advantage of the fact that the high intensity of the short optical pulses will modify the refractive index such that a focussing effect is achieved. Finally, having developed a number of devices, we will be in a good position to apply them to nonlinear microscopy of biological cells and demonstrate that the high repetition rate of the pulses provides advantages in terms of producing high optical signals without causing damage to the specimens under study.

Planned Impact

UK and worldwide photonics industry will benefit from the research outputs of this proposal as they will learn about our advances in multi-GHz ultrafast lasers from our publications, conference papers, web sites, and articles in a 6-monthly newsletter (the Light Times) circulated to a broad range of academics and industrialists. We will specifically target conferences that have both high academic standing and a large industrial attendance, such as CLEO Europe Munich and CLEO USA. UK industry in particular will have the opportunity to commercialise the laser devices as we plan to set-up a UK-based impact panel that will inform us of end-user requirements and aid knowledge transfer. In the first instance, we will look to our project partners, Elforlight Ltd (a commercial sector SME), as a route for transferring technology to UK industry, giving them the opportunity to license the generated intellectual property in the in accordance with our collaboration agreement. We believe the timescale of our project (3-years) is realistic in order for us to realise this immediate benefit through technology transfer. The impact panel will also have members who are more concerned with the application of the proposed devices such as Dr. Helen Margolis from the National Physical Laboratory (as potential public sector users of the technology in the area of optical metrology) and Robert Forster from Nikon UK Instruments (as a potential expoiter of the technology in the area of biomicroscopy). Through our regular meetings with the panel we will be informed of their end-user requirements, which will guide our research so that it is of the most benefit to them and other researchers in their fields. The timescale for these users to benefit will be longer (~5 years), as further work would be required to optimise the devices (such as stabilisation requirements for optical metrology). However, these users could take our work as a starting point for further investigation or indeed further collaborative funding could be applied for to realise these applications. In the longer term (10 years and beyond) the general public will also be beneficiaries as the application areas for our ultrafast devices are of relevance to both healthcare and telecommunications, thereby enhancing quality of life. The staff working on the project will have a full range of professional development courses made available to them by both institutions. In terms of research skills the postdoctoral researchers and student will benefit from gaining experience in ultrafast lasers and technology, waveguide devices, and in photonics cleanroom fabrication skills. They will also benefit from involvement in a collaborative project with strong potential for knowledge transfer. These research and professional skills of of high relevance to potential future employmers in all sectors.

Publications

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Description In this grant we demonstrated a series of compact waveguide laser devices that produced ultra-short (femtosecond) optical pulses at very high repetition rates (up to 15 GHz).
Exploitation Route Ultra-short pulses have become invaluable tools for imaging in bio-medical systems, for example to help in detection of various diseases, and these devices offer a highly compact sources with which to carry out such investigations. The high repetition rates may be useful in increasing the signal to noise ratio in such imaging systems without risking damage from increasing the pulse intensity.



Future power scaling in integrated waveguide geometries from the current ~100mW level to ~100W will make these very interesting sources for materials processing, such as marking and drilling etc., and again their compact nature will be attractive for industrial solutions. Such pulses of light may have applications in areas as diverse as optical metrology, bio-medical imaging, and materials processing. We have published widely on these results and so they are available to the general public. We have also obtained a further grant which will concentrate on the power scaling these devices so that the materials processing applications may be realised. This new grant involves two UK laser companies who would be well-placed to bring these devices to market.
Sectors Digital/Communication/Information Technologies (including Software),Healthcare

 
Description EPSRC Doctoral Prize
Amount £40,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 03/2014 
End 02/2015
 
Description Universitat Rovira i Virgili 
Organisation Rovira i Virgili University
Country Spain 
Sector Academic/University 
PI Contribution We have collaborated on waveguide structures in Yb-doped KYW. We have etched planar-film samples grown by our partners to produce channel waveguides and demonstrated laser action.
Collaborator Contribution Our partners grew the Yb-doped KYW films.
Impact Two journal papers and four conference papers
Start Year 2012
 
Description University of Pitsburgh 
Organisation University of Pittsburgh
Country United States 
Sector Academic/University 
PI Contribution We worked with the University of Pittsburgh to develop graphene based saturable absorbers to act as mode-locking devices in waveguide lasers. Our role was to experimentally demonstrate their use as mode-lockers.
Collaborator Contribution Pitsburgh's role was to grow the grapheme films.
Impact We have published one paper (after the end of the grant) in Optics Letters, and two international conference papers.
Start Year 2013
 
Description University of St. Andrews 
Organisation University of St Andrews
Country United Kingdom 
Sector Academic/University 
PI Contribution We have collaborated with the University of St Andrews on fabricating and operating ultrafast waveguide lasers
Collaborator Contribution The University of St Andrews have brought their expertise on ultrafast lasers to our joint project on ultrafast waveguide lasers
Impact The output from EPSRC grant EP/H035745/1
Start Year 2010